The invention deals with a method for purifying cooling liquids used for cooling and/or for lubricating, that are interspersed or loaded with metallic and/or other material impurities, especially for separation of rolling scale and oily or greasy substances from industrial process or efflux water in open cooling circulation cycles or systems in the iron or steel industry, especially in rolling mills. This invention deals also with a pertinent purification installation or plant for performing the method.
From year to year higher requirements concerning the chip removal output or the shaping output and very high requirements concerning the quality of the surface are specified for the products which are processed by the different processing methods in the machining as well as the non-cutting shaping or deformation technology. The heat generation arising during the chip removal output or during the non-cutting shaping output must be held within limits, for which reason cooling is required in most cases in order to keep the temperatures constant during the processing operation. With the required surface smoothness or quality, care must be taken that particles which have already been removed are rapidly and completely conveyed away from the machining or processing points. Especially in the case of chipless deformation technology, for instance in rolling mills care must be taken that the surfaces do not contain any solid foreign materials in the regions where the shaping tools or the rolls of a rolling stand come in contact with the workpiece, since otherwise these are rolled into the material of the workpiece and the charge involved must possibly be completely scrapped. The cooling and lubricating agents are therefore continuously contaminated with a fine dust or grit from the shaping process. In case of lubricants, aging products are additionally formed. Since these cooling and lubricating agents consequently are continuously enriched by fines or grit and other contaminations, they must be purified. The process behavior and the useful life of these media are considerably improved not only by a thorough and continuous purification of the cooling agents or lubricants, but the overall results of the machining and the chipless forming technology are optimized.
A listing of different individual machines or of individual separation arrangements such as sedimentation tanks, hydrocyclones, centrifuges, separators, band filters, pressure filters, sedimentation filters is enumerated in the Technical Information, 68th year, Vol. 7/8, 1975 dealing with cooling lubricant care and its purification as well as with separation of waste emulsions. However, no pointers are provided as to how these individual machines must functionally interrelate with each other in order to attain optimum purification results, for instance in rolling mills for the open cooling water circulation cycles used there. The diagrams shown in this publication, dealing with a sedimentation filter installation for grinding oil purification or the therein explained diagram of a thermal emulsion separation installation or an ultrafilter installation for separation of emulsions, are not suitable for use in a rolling mill environment.
An installation for purification of liquids or liquors in rolling mills containing contaminants, residues and/or aging products is known from the DE-OS 36 16 426. The contaminated liquids used for cooling and/or lubrication in rolling mills are, to begin with, collected in a collection tank and are plumped from there towards several diaphragm filters which are located in a reverse flushing cycle and are cyclically activated. The filter outputs of the diaphragm filters lead to a presetting tank, from which the purified liquid can be drawn off by means of an initial pump and be directed to its intended use, for instance to a rolling mill to be cooled. A separate precipitation vessel is provided for purifying the highly contaminated liquid passing through the diaphragm filters during the flushing process. The contaminants deposit or accumulate on the highly sloping base of this precipitation vessel and are directed to the lowest point of the base so that they can be conveyed away from there by a drawing off device. Overflow troughs or ducts are provided in the upper region of the precipitation vessel, into which the liquid precleaned by the precipitation can overflow. The liquid collected in the overflow troughs is at least partially pumped back by a pump in a regulated manner to the diaphragm filters and serves there, as a reverse flushing means for cleaning or purifying the diaphragms arranged in the filters. The water management in rolling mills can be largely automated by means of such a purification installation and the cooling agent circulation cycle, characteristically open in rolling mills, can be operated with clearly lower losses.